text:
What is APS (Aircraft Prepared for Service) Weight? What does it include?
I am looking for a complete explanation of what APS weight includes and how is it different from Dry Operating Weight and Basic Weight.


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Who owns the Concorde name?
I don't know if this is the right forum for this question but the users on here seem very knowledgeable on all things regarding aviation.
I was wondering what company owns the Concorde name as I guess it's trademarked still. I am only asking this as Lego offer a Concorde model and on the box it has printed "Airbus". I always thought Concorde was a joint partnership development between Sud Aviation and British Aircraft Corporation. It seems over the years that these companies either merged or got brought out as Sud Aviation became Aérospatiale which became Airbus. Same with British Aircraft Corporation that became British Aerospace which is now BAE Systems. I assumed since it was a joint partnership both companies would be able to use the name Concorde, unless I am mistaken and one company had more involvement in the project then the other.
I thought they would have printed both "Airbus" and "BAE Systems" as these are the modern incarnations of the two original companies that were involved in the development initially. I mean anyone who doesn't know of the history of Concorde might just assume Airbus had solely produced the Concorde which is a wrong assumption and doesn't fairly acknowledge the British involvement in the project.

You can google about trademarks. The data is public, and nobody own a name in general: trademark are limited on specific fields. (Latex, Linux, Unix have also a trademarks on texile industry). On merge and split, for sure they agree on what will go where, including trademarks: I expect Airbus got it, and it required to add his name as free publicity, in order to use the name). Just speculations, for sure legal teams of both companies got involved and they should know better compared Internet.

Airbus owns the Type Certificate (TC) for Concorde as well as the brand name (thanks to Giacomo Catenazzi for the link). I'm not a lawyer, so I cannot comment on who else is allowed to use the name Concorde (feel free to ask that on Law.SE).
The TC was originally owned by Aérospatiale (created by the merger of Sud Aviation and others in 1970) and British Aircraft Corporation (BAC), but was then transferred to Airbus:

The legal term for the firm is now the “type certificate holder”, in the case of Concorde this was jointly held at first by BAC and Aerospatiale, the two companies that built the airframe. They later past the TC on to Airbus SAS, of which both companies held shares.

(heritageconcorde.com - Concorde Type Certificate and Airworthiness)
At this time, Airbus was not the same company we know today. It was a consortium created in 1970 by several European aircraft companies which continued to exist as separate entities:

The current company is the product of consolidation in the European aerospace industry, tracing back to the formation of the Airbus Industrie GIE consortium in 1970. [...] In 2001, Airbus Industrie GIE was reorganised as Airbus SAS, a simplified joint-stock company.

(Wikipedia - Airbus)
Initially, only Aérospatiale formed part of the Airbus consortium. However, British Aerospace (created by the merger of BAC and others in 1977) joined in 1979:

In 1979, BAe officially joined the multinational aircraft manufacturer Airbus and acquired a 20% share in the venture, the move effectively reversed a decision made ten years prior in which the UK government had withdrawn its support for the Airbus consortium.

(Wikipedia: British Aerospace)
When Airbus was restructured into its modern shape in 2001, parts of the new company BAE systems (the successor to British Aerospace since 1999) were incorporated into Airbus:

BAE Systems inherited British Aerospace’s share of Airbus Industrie, which consisted of two factories at Broughton and Filton. These facilities manufactured wings for the Airbus family of aircraft. In 2001 Airbus was incorporated as Airbus SAS, a joint stock company. In return for a 20% share in the new company BAE Systems transferred ownership of its Airbus plants (known as Airbus UK) to the new company.

(heritageconcorde.com - Who built Concorde?)
Airbus continues to hold the Concorde TC even after its retirement:

Safety rules require every plane to have an air worthiness certificate to keep flying and Concorde’s was held by Airbus. It monitored any safety modifications to the planes and provided technical advice to BA engineers. Airbus thought Concorde should be grounded for good at the end of October 2003 and was unwilling to pass on the air worthiness certificate to another company.

(heritageconcorde.com - Concorde Retirement 2003)
BAE systems then sold its shares of Airbus to EADS (the Airbus parent company, now called Airbus Group) in 2006:

In 2006, EADS acquired BAE Systems' remaining 20% of Airbus.

(Wikipedia - Airbus)
Even if Airbus does not have British partial ownership any more, it continues to operate facilities in the UK, so the British heritage of Concorde isn't quite lost if you ask me :)

About trademark, official sources: https://branddb.wipo.int/en/similarname/brand/WO500000000270598?sort=score%20desc&start=0&rows=30&asStructure=%7B%22_id%22:%22bad5%22,%22boolean%22:%22AND%22,%22bricks%22:%5B%7B%22_id%22:%22bad6%22,%22key%22:%22brandName%22,%22value%22:%22Concorde%22,%22strategy%22:%22Simple%22%7D%5D%7D&_=1724849626707&fcstatus=Registered&fcniceClass=12&i=2 (and BTW Just Concorde has huge list of active trademarks as expected with a common french word

@GiacomoCatenazzi thanks, I added the link to the answer!

source: Stack Exchange

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sort: votes


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Where could I find the FOD examples of C17?
I want to find some FOD examples of huge planes in reason of ground vortex,where should I  go to search?

What does "FOD examples" mean?

@CrossRoads Presumably, examples of incidents involving foreign object damage.

How does "Ground Vortex" come into play? A just departed plane would create a vortex that could drift down. ATC makes planes wait to depart behind one in order to give any vortex a chance to dissipate.

@CrossRoads I think they're referring to the vortex that forms on the ground towards the intakes. A Google image search for c17 ground vortex shows the phenomenon.

The NTSB search might bring something up still.

You can search the National Traffic Safety Board here
https://www.ntsb.gov/_layouts/ntsb.aviation/index.aspx
as a starting point.
Under Aircraft:Category, select Airplane.
Under Model, Select C17.
Scroll down and select  Submit Query.
There are couple of hits on C17s on the first page of results, I didn't look at  further pages.
Try this stack exchange link also on the same occurrence, but not just limited to C17s.
How does this vortex form inside a jet engine?

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How do the compressor stages keep spinning after start in a free turbine?
In a ‘free’ (or uncoupled) turbine engine (specifically the Rolls Royce C20-250), what is spinning the compressor blades (N1) after start? It can’t be N2, because it’s a free turbine. I don’t think they’re freewheeling, because otherwise how would I get bleed air? And I’m pretty sure the combustion chamber is ahead of the N2 stack, so N2 wouldn't have its own compressor wheel and if it did, I wouldn't have clean bleed air.

With "after start", do you mean during normal operation?

Yes.  I now realize that the compressor shaft and the Ng spool are on the same shaft, so I now have the answer to my question.

In a C20-250 engine the compressor section is driven by the high pressure turbine (Ng spool, not N1) independent of the power turbine.  The power turbine drives the gearbox and subsequently the output shaft via a concentric driveshaft to the gas core spool.
I believe you’re confusing the configuration of this engine by assuming that all free turbine turboshaft engines are laid out similar to a PWAC PT-6 engine.   While the PT-6 design certainly excels in terms of simplicity as well as modularity for ease of maintenance, it is not necessarily the only configuration for free turbine engine. Plenty of other free turbine turboshafts have other unorthodox layouts but all operate according to the same principles.
A cutaway of the C20-250 engine appears below.  Note the non-axisymmetric air channel carrying air from the last stage of the compressor section to the aftmost part of the engine for introduction into the single can-type combustor.

I don't think there is much to confuse with PT-6, because in the relevant sense the layout is the same: high-pressure turbine drives the compressor, low pressure turbine drives the output shaft in both.

It's a turboshaft engine, so almost all the power from the gas stream is converted into rotary power for the output shaft. All the power, minus the power required to drive the compressor. The HP turbine drives the compressor (N2), the LP turbine drives the output shaft (N1).

what is spinning the compressor blades (N1) after start?

The gas stream hitting the HP turbine is.

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Is it OK to greet ATC?
My instructor told me that courtesies are forbidden in radio communication, however, we usually start conversation as "Turany Ground, OK-ABC, good morning, (... request)".
I find it natural. Is that acceptable violation of the rules, or could it cause some troubles?

Listen to a few of the feeds on LiveATC.net - for example, KORL with Executive Tower and Orlando Approach - you'll hear all sorts of this, both controllers and pilots. I think it helps transitions work better.

But also... you should wait for acknowledgement before rattling off a long request.

It is not part of the standard phraseology by any means, but it is fairly common, as is a very quick pleasantry when changing frequency.

[station name], Good morning, G-ABCD, [request]

and

G-ABCD, changing to [other station] thanks for your service.

The thing to remember is to not choke up a busy station with overuse of non-standard comms, and therefore to remember when it might be inappropriate to stray from the standards.

It really depends on the location as well. In the UK I rarely greet ATC, but when I fly to France, or Belgium I always say Bonjour and Merci as that seems to be common practice. In Ireland they're pretty friendly as well, and rarely that busy, at least where I've flown to.

It's fairly common in the UK. Was also common in SoCal when I flew there.

SOP I'm learning is simply state your callsign and wait for acknowledgment, but I'm sure if you talk to the controller a lot you become more friendly with them if it's quiet.

Listening in to ATC in Vegas, I heard a pilot sign off with "may the force be with you" - I suspect that definitely isn't standard terminology.

Is this why it's called civil aviation? :D

@Jamiec is there any argument to say that a greeting helps ATC distinguish first, initial contact from a pilot? Particularly regarding non-flight plan, VFR flying - free-calling from one station to another?

@ob318 I don't think so TBH. A first contact is distinguished already from an ongoing convo.

Technically you are not suppose to and for the greatest safety, internationally recognized vocabulary should always be used.
However, I have noticed most heavy pilots and many controllers do a greeting. That is the difference between the ideal world and the real world. I doubt being the 65th pilot to say "good morning" improves your handling or makes the controllers day any brighter. With so many pilots and controllers doing it, it really has become a matter of personal preference.
One advantage to doing a greeting is it gives the controller a one second warning to prepare for a communication. Some aircraft are equipped with VOX (voice actuated transmission) circuity that tends to cutoff the first syllable of a transmission and a greeting gets the VOX turned on.
I believe disingenuous "thank you's" and "I love you's" dilute the meaning and sincerity of the words. If a controller really does something special (I have had two occasions my life was saved), then I use sincerity, "thanks that may have saved my life...", or "your professionalism is appreciated...".
I learned to fly from the US's second busiest airport so being brief and concise was a safety survival tactic on Saturday mornings - most pilots learn to fly from a much more relaxed environment.

In particular, a one second warning that primes the controller to expect a communication from a new aircraft that's not yet on their board. I would rather add one second to my initial transmission than spend ten going through the "Last aircraft to call, missed your numbers, say your callsign again" routine.

ATC usually remarks "g'day" when transferring someone (or apparently quite a range of local colloquialisms, depending on location).

I read "heavy pilots" and was thinking "why only obese pilots, are they friendlier than skinny ones"...

Personally, I believe that your life being saved is a bit high a bar for doing something special that can warrant a thank you without diluting the meaning and sincerity. YMMV.

While it is true they probably saved my life twice, it is also true that had I followed their instructions I might be dead 3 times more than that. I generally don't commend them and for the same reasons I don't curse or scold them when they make a mistake. For me it is "just business" with lives at stake and professionalism is the best way to handle everything - no matter what.

They are not “forbidden” but it’s not standard phraseology.  Most times common pleasantries are inert and generally either go unnoticed or mutually exchanged by the aircrews and ATC.  There are instances, particularly in high density airspace where it can impeded communications and it’s not appreciated.  Flying an aircraft into Oshkosh, WI for the annual EAA Expo is an excellent example.  Here you may not even be identified by your tail number and given very brusque instructions and expected to comply with a minimum of chatter. Eg “Blue and white Cessna, land on the thousand footers. Rock wings.  Red Cherokee, follow the Cessna on final, land on the numbers.  White experimental, turn base now....”


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Is N1 and N2 and any N speed the revolutions per second for the rotor blades of compressors?
For example the Airbus A350 has three N speeds I think is called Nucelle speed and N1 is for the fan or LP compressor, N2 is for the IP compressor and N3 is for the HP compressor. Even on the Airbus A320 with N1 is the L.P. compressor and N2 is the HP compressor. But anyways is the N speeds how many revolution per second it's doing or What?

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Does the 737 have a higher aspect ratio than most later 7X7's?
In this video:
The Insane Engineering of the 787
there's a chart (at around 10:40 in) which shows that the 737 (which series?) has an aspect ratio of over 9, while the 747, 757, 767 and 777 rise from 6.5 to 8.5 or so.
Is that valid data? If it is, what's the reason for that change in aspect ratio? Is it perhaps different basic shapes of the wings? Distribution of mass along the wing? Internal structure within wings?

According to www.b737.org.uk, the aspect ratio of the Boeing 737 increased from 8.83 for the -100 and -200 to 9.45 for the NG models (-600 to -900ER) while span increased from 28.35 m to 34.32 m. For the MAX, the wing span grew to 35.92 m and the aspect ratio to 10.16. The main reason is the higher price of fuel at the time of development of the more modern models which dictated a shift from a lighter wing to more efficient aerodynamics.
From this answer you will learn that aspect ratio is only the result of span and wing area, because those two parameters are the main drivers for induced drag rsp. fuel volume and are actively optimized to minimize overall cost. Today's very efficient engines allow to drive the optimum aspect ratio above 10 even for long-range airliners.
Early long range jets demanded high internal fuel volume, so their aspect ratio tends to bunch at the low end (7 for the B707-120 or the B747-100) while the 737, designed from the outset for short European and US continental routes, could afford a more slender wing. At the time of development of the original 737, jet fuel cost around 8 cents per Gallon. When compared to the peak in 2008, the nominal price has gone up by a factor of 50. While most fuel savings came from better engines, the higher aspect ratio of later 737 models contributed to keep them attractive for airlines (giving high rebates also helped).
To answer the question in your questions title, I plotted the aspect ratio (Y axis) over the different types (X axis) with data gleaned from Wikipedia. The higher values are for later types. With the exception of the 707, where the aspect ratio shrank from 7 for the -120 to 6.66 for the -320, the aspect ratio increased in all other cases for later variants:

Yes, the 737 started life with the largest aspect ratio of all Boeing  airliners but the aspect ratio of the 777ER, the 787 and the 777X is higher than that of the B737 Next Generation (-600 to -900). However, the span increase of the B737 MAX let it take the crown back. The general wing shape, mass distribution or structure remain similar and have no consequence for the aspect ratio.


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When do carriers overhaul their flight schedules with flight re-numbering?
A (US domestic) carrier can obviously stop flying a flight, or some legs of that flight, for a host of reasons. But - occasionally it makes more significant changes, like re-numbering many flights, or changing a bunch of routes on offer etc.
My question is: Are there rules, or is there an established custom, regarding when this happens? Specifically, do operators always align these changes to the beginning of years, quarters, or months? Or do they just happen at arbitrary times and not even bunched together?
I'm interested in the period between 2000 and the present time.

Daylight savings time is a HUGE headache for airline schedules because some jurisdictions change over on different dates or don’t change at all. It is even worse for international flights between North and South America as the summer/winter change over dates are all over the place.

@MikeSowsun: Ok, but those are still "minor" changes: +1/-1 hours. I'm more interested in reassigning of flight numbers to different routes.

At my carrier, there are no rules along the lines asked about; the rules that apply are generated by the Schedule Planning department, and will change as they see fit. They produce many schedules each year, and how much "this" one differs from the previous one depends on lots of factors regarding fleets and markets and priorities. Some things are seasonal, many aren't.
The change-over dates are similarly "whatever makes the most sense" as the schedules are being built. One carrier may be on a 6-week cycle, with another on a calendar month cycle; ours seems to change at not entirely regular intervals. Some schedules are longer than others - mid June thru mid-August may be one fairly constant schedule, but November & December may see 4 distinct schedules, as travel fluctuates around the two major holidays.
Increasing automation over the last 20 years has probably contributed to this variability.
There may be some "sacred cows" in the schedule, that flight 1 always is the first departure from (big east coast hub city) across the country to LAX or SFO, perhaps, or flight 711 always serves Las Vegas (dice roll of 7 or 11 is a winner), etc. But much of the schedule is, whatever makes sense to the planners this month or this quarter or this year.
The closest you'll come to having predictable guidelines would be to study one airline's schedules over time & observe enduring patterns... but even those may not be written in stone.


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Were my airplane's wheels under-inflated?
I recently took a flight on a (Lufthansa) Bombardier CRJ900 aircraft. As I was about to embark, my eyes caught this image:

And the aircraft wasn't even loaded with the passengers yet. If I saw this in a car, I would assume a flat tire or other loss of air pressure...were these wheels under-inflated?

Hmmm, I don't see where this tires are flat... Those are no bike tires, which touch the ground with a coin-sized patch.  Instead, they should touch the ground with the full width of their treads.

Not sure why you think this has anything to do with a car's tires... If the aircraft is fully loaded that's the way they're supposed to look. And there's no air in there, it's nitrogen.

@Squareoot: Make this an answer, perhaps?

@JuanJimenez He says in the question, passengers weren't even loaded yet.

Doesn't look abnormal to me

@selectstriker2: If you can back that up with an argument regarding why it's normal for tire bottoms to be spread out on the tarmac - please make that an answer.

I just compared them to other pictures of crj900 landing gear and they all look that way. Not very scientific though.

@selectstriker2: Links to such pictures, then?

Passengers are quite a small proportion of take-off weight, compared to the airframe itself, the fuel, and the hold cargo - certainly small enough that they won't make a visible change to the tyre's shape.

High tire pressure means less rolling resistance at least on a good road. However it also reduces grip that makes braking less efficient (source). Hence high pressure may make sense for a bicycle but not for a plane where the power is more than abundant.

Another factor might be mileage. A plane usually travels only a short distance on its wheels, in contrast to road vehicles. So for a plane you could allow yourself a lower tire pressure to gain braking efficiency for the cost of a little bit more wear. For cars underinflation would be a bigger problem.

Neither car nor aircraft tires are supposed to be inflated to the point where only a small percentage of the tire is in contact with the ground. If you can think of a scientific argument why they should be, post it. It's very common knowledge that inflating tires to maximum pressure reduces sidewall effectiveness and overall tire performance.

What is "sidewall effectiveness"? Also, I didn't talk about maximum pressure, which is not good for cars either, but it seems strange to me that so much of the tire would be on the ground.

A tire is not a 100% rigid device. They are made of synthetic rubber because they need to give. When there are any sideloads on the tire, the surface that provides contact with the ground to give you control and traction is the tire's sidewall. In tire engineering parlance, it's called "lateral stability."
As to max pressure, inflating the tire to the max rated pressure is the only way to get the visual effect you want, which in 99% of cases is the wrong situation you want in any tire.


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How does the debris rejection system in the CFM LEAP engines work?
How does the debris rejection system in the CFM LEAP engines work?
LEAP - The debris rejection system

It's an inertial particle separator system incorporated into the compressor inlet.  It forces intake air to follow a curved passage that makes particles with mass sling to the outside of the duct due to the sudden change of direction, where, when required, those bypass ducts open into the stream to dump the particle laden air overboard.
Turboprops have used inertial particle separators that can be opened or closed for eons; this is the first time I've seen the concept applied to a jet.  It's desirable for turbojets and turbofans to have an inlet that's good at "catching" air for a good ram effect; better for efficiency and a strong ram effect makes the engine windmill well (important for re-light capability).  Problem is, strong ram effect also means a lot of particles being ingested.  While large objects like birds are an obvious factor, with jet engines there is actually a more subtle long term problem, sand particle ingestion that literally sandblasts the compressor blades over time and shortens the life of the engine.  This is a huge problem in desert operating environments.
Some engines like early versions of the GE CF-34 used a compressor inlet profile that was "flush" to the airflow downstream of the fan, which tended to encourage particles to pass on by in the fan discharge. This was a design goal for the A-10 Warthog, for which the engine was originally designed, and made it fairly FOD resistant.  Similar variants were used in the Challenger business jet and the CRJ200 Regional Jet.
Problem was the ram effect was low, which made it windmill poorly (you have to maintain a fairly high speed if it flames out, to keep the core of the engine from stopping - the dreaded "corelock").  On later commercial variants, the compressor inlet profile was revised to present a more direct into-the-flow inlet for the compressor, improving efficiency and making the engine able to windmill at low speeds.  The price of this was the FOD resistance was reduced and in sandy environments the erosion wear problems went way up.
This design appears to be an attempt to keep a compressor inlet profile with a good ram effect while providing the ability to minimize sand ingestion when required.  The benefit is decent engine life for operators in sandy environments.  Middle eastern airlines would be very keen to have this feature because they tend to suffer from short TBOs from their engines getting sandblasted.

The forces at work are centrifugal forces.

Which derive from inertia...If I used the term "centrifugal", people would infer from that that the airstream is being spun around the engine's axis, when it's just a minor couple of changes in direction of a flow moving axially that's going on here.

Inertia is the better term.


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Does "nose dive" have a technical aviation meaning?
I've usually heard the term 'nose dive' used in a metaphorical sense -- "Wow, your stock portfolio is really in a nose dive!"
Does it have any legitimate aviation meaning?
More specifically, is it redundant?  Are there types of dives which do not involve a nose-down attitude?

I'd say 'nose dive' and 'tail spin' share two qualities: nonstandard terminology (for 'dive' and 'spin'), and invariably negative connotations, though either may be a deliberate manoeuvre.

Are there types of dives which do not involve a nose-down attitude?

Yes (although these are not always intentional): a graveyard spiral can occur without a nose down attitude. You can also stall a plane nose high and begin diving to the ground maintaining a stalled nose high attitude, this is similar to what happened to AirFrance 447. A flat spin will also result in "falling" vertically with a relatively flat nose attitude.
In my experience "nose dive" and "dive" are generally interchangeable.

Maybe a matter of semantics, but I would not refer to a stalled nose high descent as a dive.  And I certainly wouldn't call it a nose dive either.  Dive implies going head first.  Think of jumping into a swimming pool vs diving.

"DIVE DIVE DIVE" makes me think that perhaps it was originally a submariner term, as it would make more sense in that context -- but that rather takes us out of the scope of this SE.

It does if the TCAS system is equipped with the klaxon horn option; AOOOOOGA   AOOOOOOOGA   DIVE...DIVE.. DIVE.   Make sure the conning tower hatch is closed though.

@Bianfable my head must have been elsewhere, I removed the TCAS reference as it is indeed incorrect.

Does it have any legitimate aviation meaning?

Yes.  It appears occasionally in FAA accident reports.

Is it redundant?

In all of those appearances, yes, technically.  "Dive" would suffice.
No, as an (unintentional) rhetorical device.  The phrase often used here is some variation on "took a nose dive," which betrays the informality of the writer or the interviewee.


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What are the names of these aircraft? Part.2
The next part of the group... Can someone help me?

Would it be better to ask a separate question about each plane? That way each will (hopefully) have a single definitive answer.

Yes, please do make these one question per model. (Though if you have multiple pictures that you believe represent the same type of aircraft, it probably won't hurt including all of those in a question for that model.)

The last one is an Antinov AN-2

(source)
The first one could be the Gee Bee Y Sportster

(source)

Concur on the Antonov, but the shape of both the tail & the engine cowling is pretty different from the Gee Bee’s.

@RalphJ I agree the models tail is pointier and the Gee Bee has a cowling enclosure but I have built models that are not always exactly accurate so it was just a guess.

First one may be a Ryan PT22 trainer, used for basic pilot instruction in WW2 by the USAAF and USN. Those flying today tend to be turned out in polished aluminum with yellow wings, the original colors of the trainers. Not long ago, Harrison Ford deadsticked a PT22 onto a golf course when it's engine quit.
Third one looks like an earlier Travel Air, maybe a model 4000, fitted with wing spotlights for air mail service. Travel Air was the original company of three light plane legends: Clyde Cessna, Walter Beech, and Lloyd Stearman.


text:
What closed-cockpit biplane is this model modelled after?
What closed-cockpit biplane is this model modelled after?


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What flying machine is this model?
Help with this flying machine. I think it is a concept / prototype designed in Europe in the nineteenth century.

Leonardo daVinci?

A friend sent me this. Thanks for the answers.
Gull-wing by Werner Siemens, Germany 1847.

Yes, I have another source for that sketch by Siemens [Rockets, Missiles and Men in Space, Willy Ley. Signet Books, New American Library, 1969] https://imgur.com/4jY8II3  https://imgur.com/aCiwhis

It may be the  "la barque ailée" as exposed in the Bourget air museum

It is probably an imitation of Leonardo da Vinci's flying machine. As you can see from the following picture


text:
What trimotor is this model?
What trimotor is this model?

(own work)

Are you sure that's a real airplane? The vertical stabilizer seem far too small.

I believe it's the French Couzinet 71 'Arc-en-Ciel'
https://www.hydroretro.net/etudegh/arc-en-ciel_atlantique_vol1.pdf

Not quite - I think it is the Couzinet 70. The radiators of the model look like those of the Hispano-Suiza engines of the Arc-en-ciel III. The linked PDF is a great find!

What an interesting but tragic story...


text:
What twin engine is this USAF-painted plane?
I keep trying to identify a group of aircraft, what bimotor is this plane?

(photos: own work; click to view)

(wikimedia.org) A T1 variant.
It appears to be a British Aerospace C-10A or Jetstream 3M.

In order to improve sales prospects in the US, the fifth prototype was fitted with the US-built Garrett TPE-331 in place of the French Astazou. Changing to the US-built engine was enough to allow the United States Air Force (USAF) to consider it for cargo use. It eventually placed an order for 11, fitted with a cargo door and accommodation for 12 passengers or six stretcher cases, to be known as the C-10A, or Jetstream 3M. The USAF cancelled its order in October 1969 citing late delivery.

From https://en.wikipedia.org/wiki/Handley_Page_Jetstream
and it sounds like none may have been actually built.
See http://www.aerospace-technology.com/projects/turboprop/ for more info.
In the 1980s I remember them being a successful civilian commuter design. However, they were slow compared to the Fairchild Swearingen SA-227 Metroliner, a major competitor, and suffered from a lack of baggage capacity. They somewhat mitigated that by having an optional belly cargo carrier on them, but that slowed them down even more.
I was flying the SA-227 at the time for Horizon Air. Over the route from Redmond, Oregon to Portland, Oregon, the Jetstream (I can't remember the carrier's name—they eventually ceased operation), would leave a few minutes before us, but we would always overtake them and land in Portland before them.
For a time, over routes they shared with us, they would send the bags they couldn't carry over to us under a reciprocity agreement since we had ample baggage capacity. Eventually Horizon Air required them to pay since it was turning out to be a one way agreement, they never having any spare baggage room.

Surely they could have put baggage space in that outrageously long nose. ;-)


text:
What was the aerial chase scene plane in 'Murder in the Clouds'?
I spotted this aircraft (tail number NC-406N) in an aerial chase scene in the movie Murder in the Clouds (1934) on Turner Classic Movies.
It appears to be a Travel Air D-4000. Is this correct?


text:
What is the unit for ground speed reported by ADS-B?
Strangely enough, I'm having trouble finding the unit reported by ADS-B on the Internet. Many sites simply refer to it as "ground speed". Is it measured in KPH?

FWIW, I googled "ADS-B goundspeed readout". The second entry that came up was for https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC20-172B.pdf. In that document, the only unit I saw for distance was nautical miles, and the only unit I saw for speed was knots.


text:
Do I need to copy old entries to my new logbook?
i just got a new logbook to replace my cheap paper cover one, just wondering if i need to copy over all the logs(that my instructor wrote) or just leave it and when i need to tally up my hours read two. Is there any rules saying that I cant copy  logs that someone besides me wrote? Should I carry both with me?

Welcome to aviation.SE! Can you tell us which country you're asking about? Regulations and best practices are different in different places.

The following information is pertinent to the FAA in the US and additional information is on their website. AOPA provides this guidance.
...Each person must document and record... in a manner acceptable to the Administrator... Persons must present their pilot certificate, medical certificate, logbook, or any other record required by this part for inspection upon a reasonable request 14 CFR 61.51 - Pilot logbooks (Copies of you log are acceptable by the FAA administrator.)
Your medical and Pilot's license are the only documents required to be carried with you. It is suggested that all other records be kept in a safe place. Insurance companies have been known to deny claims when the records are destroyed in a plane crash.
Electronic or written records are permitted so copying or transferring is legal. To legally act as PIC, a private, commercial, and airline transport pilot must have a current medical certificate and have all required endorsements, ratings, and recency of experience for the type of aircraft being flown and the flight conditions under which the flight is conducted (see FAR 61.3, 61.31, 61.56, 61.57).
It has been popular to transfer and use electronics means for over 25 years. About the only thing the FAA does not track is recency requirements such as IFR or night currency and a signed copy is only required until it runs out - after which the information can be transferred to other written or electronic form. I imagine most pilots don't keep a signed copy of recency experience and if the FAA requested it, they would pencil whip a copy to them.
While electronic records hold the same legal validity as paper, it seems to me hand written documents are less likely to be disputed. I prefer paper, but I scanned my old logbooks onto multiple computer backups just in case something ever happened, i.e flood or fire.
If paper or electronic storage is destroyed, the pilot is required to make an entry with their best guess. I know of an airline pilot that had his baggage stolen in Japan with his cell phone containing several months of data; he simply made a new entry with a guess.


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Could an electric airliner be aerotowed to cruise altitude by an electric "tug" aircraft?
The low energy density of batteries make electric aircraft need a high ratio of battery to payload. Take off and climb to cruising altitude could account for a substantial fraction of the energy required for a short haul flight. The point of aerotowing would be be to have less battery (and maybe motor?) requirement and more payload in the towed craft for cruise and landing whilst the tug aircraft could return to the take-off point. There would be the downside of needing to handle the tug landing of course.

At this point in technology, I think it would take more fuel/energy to "tow" the aircraft to altitude than it would to just burn the fossil fuel necessary to do so, meaning the batteries in the tow aircraft have to be recharged from something, nothing is free. The power/density of fossil fuel is still unmatched in the battery world.

An alternative would be to have the "tug" give power to the airliner through an electric cable, rather than towing it. Either way, I think this is a really interesting idea; I look forward to seeing the responses.

Thanks Ron but the idea is not to use less energy, much less get something free, but to potentially have zero-carbon airliners.

Have you seen this recent article discussing plans by Boeing, Airbus, and others for short haul all-electric planes?  https://techcrunch.com/2018/07/08/the-electric-aircraft-is-taking-off/  I just wonder - what is the fuel source to make all the electricity to charge the batteries?  There are losses in making the electricity, losses in charging the batteries, losses in efficiency in cooling the motors, etc.

And another, Zunum Aero, proposing hybrid to start and full electric in the 2020s  "Did you know that short-haul flights produce over 40% of aviation emissions? With our aircraft, we believe these will be largely eliminated within twenty years. Our aircraft are “hybrid-to-electrics” that sip fuel only when they have to, will use even less over time as batteries upgrade, and will one day go completely without — so that flying will be kind to the Earth."  https://zunum.aero/#About-us

Yes, a tug would help, but not greatly so. If your goal is zero-carbon air travel, the tug will stretch the possible range, but the result will still be much too low for practical use.
The principle is similar to using a catapult to save the energy needed for acceleration on the ground. This topic was covered here and shows negligible gains. We also have covered the problems of fully-electric airliners and the weight disadvantage of electric engines, so I will not cover this here again.
If we only look at the energy needed to lift a conventional airliner to its cruise altitude, the magnitude of the problem should become obvious. Here, only the tug is electric while the airliner is a normal A320. We have lots of answers with A320 data, and assuming that less fuel is taken onboard since we get some help in climb, the take-off weight used here is 72 tons. Cruise is in 30.000 ft, so we need to lift 72.000 kg by 9144 m. Energy $E$ is mass times height times gravitational acceleration, or 1.8 MWh or 6,456 MJ. Add to that the acceleration to Mach 0.8 which is 240 m/s at altitude and we need $\frac{1}{2}\cdot m\cdot v^2$ = 2,074 MJ more.
The sum of 8,530 MJ is the energy content of 200 kg of jet fuel, but for a realistic value we need to divide that by the efficiency of the jet. The same has to be done for the electric propulsion case, but efficiency is much better here. If we assume an overall efficiency of 80% in case of fully electric propulsion, the electric energy need to lift an A320 to cruise conditions is 10,662 MJ. To overcome drag and keep systems running, we need maybe another 25% more, so the total energy need will be 13,328 MJ.
Let's consider a tug which carries half its weight in batteries and has the same take-off weight as our A320. Its 36 tons of batteries will hold 25,200 MJ of energy which is just enough to bring both of them close to cruise conditions. On its way back it will glide, so we can save the fuel for lifting the A320 up. How much is that? If we assume an overall efficiency of 33% for jet propulsion, the savings are 600 kg or one twenty-fifth of overall fuel consumption over a 5000 km trip.
Even with the better efficiency of electric propulsion, a heroic effort is needed to save a comparatively small amount of jet fuel. It does work, but the gains are small compared to the effort needed - just consider that the turnaround time for the tug is similar to the flight time of our A320, so as many tugs as A320s are needed to make this system work for all flights.


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UAV development platform
What is UAV development platform? For example, STM UAV, Intel, Parrot and so on. I searched on Google, but couldn't get its exact meaning.
Thank you very much.

Are you only interested in commercial platforms? There are open source platforms too that may be easier to study, in particular PX4.

This is a fairly broad question, can you narrow it down a bit and perhaps tell us what you are developing a UAV for and what you are looking for in a platform? FWIW with enough engineering effort anything can be used as a development platform.

I want to develop micro unmanned vehicle (MAV), so I would like to know which MAV platforms are exist and what is UAV development platform (is it only hardware, or only software or both of them)?


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I would like to fly from the Aleutians to Japan
I would like to know what is required to do this... what is the legal... what kind of fuel would I need to make the trip in say a 172XP Hawk.
Has anyone done this and what kinds of procedures should I be reading up on?
Where would be the best place to land once I reach Japan?

Hello Neeraj Maruka, welcome to aviation.stackexchange.com. Your question has many aspects: legal side, selection of airports, route planning, aircraft selection, fuel planning, contingency planning etc. That is too broad for one answer. Consider to break it up into multiple separate questions. Also, it seems to me that if you can't answer some of these questions yourself (e.g what kind of fuel do I need), you don't have the required experience for such a long over water flight, and you will be exposing yourself to a lot of risk.

Thanks for the reply. I realize now that my question about fuel was misleading. I meant the amount of fuel. I have done flights over water (nothing this long). I am trying to imagine if it is even possible with a single engine to do it, or if it would require a fuel stopover in Russia.

To get started, you may want to research single engine piston ferry flights. I know they happen accros the Atlantic, I presume it's not much different over the Pacific. They sometimes use additional in-cabin fuel tanks.

Well... in your pilot training, there must have been some lessons on flight planning? Something like select route, select cruise altitude & speed, estimate fuel flow from POH, obtain wind forecast, calculate ground speed, divide route distance by ground speed to obtain flight time, multiply flight time by fuel flow to obtain trip fuel, add reserves etc. => that much fuel. Obviously for flights where aircraft weight and relative wind changes over the duration of the flight and position of the aircraft (i.e. any sensible flight), do above for short segments and over multiple iterations.

SkyVector.com shows 1282nm from PASY, Eareckson Air Station near the end of the Aleutians, to RJCN, Nakashibetsu, Japan, the closest airport I could find in northeast Japan.
No wind, 10 gallon/hr, that's 128 gallons of gas needed. More than twice what a 172XP carries? (50, 60 gallons?) So pretty much the equivalent of 2 passengers for the fuel and tank. Don't forget the cold weather overwater survival suit, not fun to sit in bundled up for 10+ hours.
Now, if the Air Force agreed to let you land there, and agreed to let you have AVGAS brought in, and if the winds cooperated, you might be able to make it with a big ferry tank installed.
You might have better luck departing from Adak near, Mount Moffatt, PADK. 1612nm.
https://nfdc.faa.gov/nfdcApps/services/ajv5/airportDisplay.jsp?airportId=padk
The FAA site does not discuss fuel, you can check www.airnav.com for that.
Dutch Harbor, for example. Only Jet fuel is shown.
https://www.airnav.com/airport/PADU
If you had the Diesel 172, that could make the trip a little easier logistically
https://www.planeandpilotmag.com/article/turbodiesel-cessna-172-jt-a/#.XGBSDlVKjX4

If there is an eye popping spec for the JT-A, it’s the max range, 963 miles, an improvement of 323 nautical miles over the 640-nm range of the Lycoming powered Skyhawk.

That would help a lot!


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How to convert a PPL (Gyrocopter) to a PPL (Helicopter)?
If I have a Private Pilot License (PPL) for gyrocopters, and I want to convert it to PPL for helicopters, are my flight hours in the gyrocopter considered for me as flight hours in helicopters?

What country are you in?

In the US, Gyroplane and Helicopter are class ratings within the Rotorcraft category. FAR 61.63(c) specifies that the addition of a class rating does not require any specific amount of flight training time, and no more total experience than would be required for the gyroplane rating you already have, so the question is moot. All you need is an instructor willing to sign you off and to pass the abbreviated practical test.

For starters, you don't "convert" a license from one class to another; you add any new class(es) to the existing one(s) on your license.
Since many of the tasks/skills are the same across classes, though, you should only have to perform the ones that you haven't already demonstrated for the old class.  See page 1-iii of the Rotorcraft ACS in column RG for your specific case if you're in the US.  For instance, since you demonstrated you knew what to do if you got lost in a gyroplane, you don't need to demonstrate it again in a helicopter because (at least in theory) it's the same skill, whereas landing is (I assume) completely different.  Of course, it'd be wise to brush up on those common tasks anyway if it's been a while.
The minimum hours will require a detailed reading of the specific FARs.  You can use hours logged in a gyroplane to meet requirements for hours in "rotorcraft" or "any aircraft", leaving you with only the hours specifically required to be in "helicopter" as your minimum training.  You will probably exceed the latter before a CFI is willing to sign you off anyway, but you'll need to explain to the DPE how you've met each requirement and why the various hours you've logged can (or can't) be used for each, so it's worth looking over.


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Can the real time operating system used in aviation equipment be certified by itself?
Can the real time operating system used in aviation equipment be certified by itself, or must it be a part of some software certification effort?
I'm asking for getting a certificate of 178C. I don't understand if it is possible. There are a lot of resources that tell us about "certified operating system", but if is certified as a part of a project or it is certified just itself without any project... I have no practise in this field, but I was asked this question and it makes me puzzled.

A DO-178C compliant RTOS (such as LynxOS-178 mentioned by @mins) is going to have a certification package you provide along with your DO-178C artifacts for your software.
Note that there is no such thing as a DO-178C "certificate". DO-178C is a process that generates certification artifacts that are packaged and provided to the Certification Authority as part of some approval application (TSO, TC, STC, PMA)
It is also usefull to recognize that most software on equipment installed on an aircraft is not going to run on an RTOS, but rather run directly on the hardware (bare metal)

So the RTOS is certificated as part of a larger system.  I would also say that almost every avionics product I've worked on in the last 20+ years had an RTOS of some type. Some were pretty small purpose-built OSes, but it's important to have an OS to provide an abstraction layer from the hardware. Writing directly to the HW will cause major rework when the HW go obsolete - and it will. The only ones I can think of without an OS were simple controllers that were based on Programmable Interface Controllers (PIC).

IMA systems would likely use an RTOS to host various tasks/applications, which I haven't worked on. Everything else I've worked on have been custom PCBs with a microcontroller or microprocessor and custom software. An RTOS is either very expensive, difficult to certify, or entirely unnecessary for the product at hand.

IMA systems require a DAL Level A RTOS as all applications on the IMA have to operate in their own protected partitions. They are complex and expensive. But even for simpler federated products we often used LynxOS or a simple custom RTOS. The reason was to provide a standard programming API to simplify the application software and resulting changes needed when the inevitable hardware changes came along. I will agree that for some products it wouldn't make sense to go through the effort to use an RTOS.

I could see the likelyhood of using an RTOS on new projects increasing once a company has invested either in purchasing the cert artifacts for one or developing their own.


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What's Permaswage / Harrison tube repair?
In modern aircraft, damage of hydraulic tubes can be repaired by Permaswage/Harrison provided by maintenance manuel. However, What is Permaswage / Harrison? It's a name of company?

A quick google for "Permaswage/Harrison" reveals that

Permaswage is the technology leader in the fluid fitting industry providing proprietary and standard components, tooling, and training to all major aerospace companies globally.

"Harrison" seems to refer to a variety of internal swage fittings that are separable ridge tube end fittings commonly used in aerospace fluid transfer applications:

They are also referred as “Harrison”, “Stanley Aviation” or “Sierracin” fittings, due to the history of the product.

From this, I would deduce that one can use these products to effect a repair to hydraulic lines with these methods/products because:

Internal swaging is a mechanical method for the attachment of fittings to tubing. This is accomplished by forming tubing outward into grooves within the fitting.

--From the "Harrison" link


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Position update rate of GPS
GPS satellites send data at the rate of 50 bits per second. One GPS subframe is 6 seconds long. How is it possible to update one's position faster than once in 30 seconds when we require the whole frame (5 subframes adding up to 30 seconds) to extract the NavBits for the pseudorange calculation?

You might try this question at gis.SE some of the people there are experts in signal analysis.  But do keep in mind you generally need 4 satellites to get a reading and you can have up to 8 or 10 above the horizon, depending on location and altitude.

oversimplifying, 50 bits per second means there are approximately 50 opportunities for calculating some position from the signal delay. it's the timing what counts, not the actual information from the data frame.

@szulat Yes, I understand that I don’t need the entire data frame to calculate the time differences. But to solve the pseudo range equations I need the satellite’s coordinates, for which I may need the complete data frame, right?

satellite coordinates are predictable, once you get the complete initial information you can continue even though further updates are delayed by slow data transfer.

Also, a lot of "GPS" devices actually use information other than GPS as well. Mobile phones, for example, use the Internet (or the cellular network) to get most of the necessary data instead of getting it from the satellite. They use accelerometers, gyroscopes, compasses, and triangulation of cellular, WiFi, and Bluetooth signals as well. Plus, depending on where in the world you are, they also can use GLONASS, BeiDou, or Galileo in addition to GPS, so you may not only have more than the required 4 GPS satellites in view, but also a number of satellites from other systems.

Position interpolation between readings based on last positions & speeds calculated?  Plenty of 10Hz update GPS units exist, so it doesn't seem be rocket science to get there.
Units can track 12 or more satellites.  If calculations are being made from several sets of readings, then multiple positions can be calcuted at any one time as well.


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What are those things under the Concorde’s cockpit windows?
I’ve noticed there are little bits sticking out under Concorde’s cockpit windows and they’re too small to be canards. Are they some kind of vortex generator or something?

(Source)

These are called vortex panels. At supersonic speed the inner engines were starved or air so the panels were designed to create a swirl of air to feed them.
I never designed them but I wrote the cnc program to machine them. They were a sandwich of aluminium frame upper and lower parts with  aluminium  sheeting riveted over the top and bottom.


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Do airline pilots get to go home often to see their family and have a break from flying planes. If so, how many days?
Do airline pilots get to go home to see their families often, and if so how long?

Depends on the route they fly. Overseas could be every other night, domestic could be every night.

Welcome to aviation.SE! I don't know if there's a good answer here: it would depend on the country's employment laws and the airline's policies.

For US domestic pilots, it's highly variable and depends on one's own preference, their seniority when bidding for a schedule, and what their company's scheduling policy is like.  That said, many (most?) pilots go to work for between 3-5 days at a time and get between 3-4 days at home between work periods.

This depends on a lot of things ranging from seniority, company policy, routes and schedules which the pilot bids on, etc.  New FOs and Captains will work around 4-5 days then get 2-3 days off.  Senior captains on Wide Body Aircraft may get 3 days on, 4 days off with on two flight surfing this period.

I once worked with a software developer who was also an airline pilot. He would fly for two weeks, then work with us for two weeks (living at home with his family), then fly for two weeks, etc. I don't recall what sort of routes he flew.

All in the contract, routes, and choices of the pilot within that contract. Some fly trips of up to two weeks, others are back home every night if they have a home near their base airport and work regional. Some choose to take all available work offered while others stay near the minimum.
Labor law limits total flying time per day and per week depending on crew size and time of the day.

Many companies allow bidding for trips, days off etc. Company, routes, seniority, equipment flown all enter the equation that results in the answer. As stated by others, some are home every night (flying turn-arounds) JFK-MIA-JFK as an example. Others prefer less commuting to the airport and will choose 2,3,4 day trips, overnighting at different cities each night until finished with the sequence of trips. Some jobs have trips that fly for 1-2 weeks at a time, not necessarily everyday but they are gone from base that long. Also where one lives relative to the base they work at will affect how often they are home with family.


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How to find the distance if the points are above Earth's surface?
There is a lot of information online about how to find the distance between two points if both the points are on the surface of the earth. But no article mentions about how to find the distance if both the points are above earth surface. Haversine formula works only for the points that are on the earth surface. But what about points that are above earth surface?
Note: I think we should consider the curvature of the earth as well while computing the distance.

I think this question would be better served on Gis.SE. I'll wait for some others to have a look at it, but in case I will move it there.

@J.Dow: why do you think Haversine formula works only if the points are on the earth's surface?!?! It works for any sphere. Just use the right value for the radius.

@Curd Yes you are right. It works for any sphere. I was just considering the context of finding distance between two points above earth surface.


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What is the ideal volume distribution for minimization of transonic drag?
I am aware what the area rule states - my question is what is defined as "as smooth as possible area distribution" - Is there a formula for the curve?

Since Drag is proportional to S'', the key is to derive a shape that has a minimum S''.
The result is the Sears-Haack body.

The Sears–Haack body is the shape with the lowest theoretical wave drag in supersonic flow, for a given body length and given volume.

The area is given by:
$$ S(x) = \frac {16V}{3L\pi}[4x(1-x)]^{3/2} = \pi R_\text{max}^2[4x(1-x)]^{3/2}$$
And the radius is given by:
$$ r(x) =  R_\text{max}[4x(1-x)]^{3/4} $$

Image source


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Under EASA regs who is responsible for part m continued airworthiness? Lessor or Lessee?
If an aircraft is leased out by a lessor to an operator does the lessee (operator) take full responsibility of continued airworthiness or does the lessor have some liability?
Perhaps it's similar under FAA law?

It really comes down to the lease contract.  I don't think any of the regulatory authorities much care who pays to maintain it or what's in the lease contract, as long as the airplane is airworthy when it leaves the ground, which is basically up to the operator.  What we are really talking about here is who pays.
Pretty much anywhere, the lessor is expected to deliver the unit in an airworthy condition, then the lessee is expected to maintain it and return it to the lessor in an airworthy condition at the end of the lease. Like a car.  But it depends on the details in the lease.
The lessor is frequently a non-operator (Like GE Capital) who has no means to maintain the airplane in the first place so in any case it's the airline that will actually do the work, or contract the work, for something like an AD.
Who is on the hook to pay for Service Bulletins and AD compliance will be up to the lease contract (on an aircraft that is out of warranty).  If someone leases an out-of-warranty airliner from GE Capital, and the contract says that GEC will pay for ADs, then the airline will do the work but charge back the expenses to GEC.
Plus, GEC may have a clause in its purchase agreement with the OEM to cover AD costs beyond the warranty period and extend that protection to the lessee.  There are large variations in terms and conditions between OEMs, leasing companies, and airlines on a given type, as it's all part of a negotiated package.


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Does TC holder of aircraft need to be notified by the PART 21 DOH that they are making a major mod STC to their product?
Can someone confirm if a part 21 design organizations has to inform the TC holder or not? This is because I am on a part 66 course at the moment and the text is as follows in one of the books, but I'm not sure if It is true.
“The Supplemental Type Certificate will not be issued unless the type certificate holder has been informed and has expressed no technical objections to the proposal and has agreed to collaborate with the STC holder in matters affecting continuing airworthiness".
Thanks

I was many years at an OEM, in tech support engineering, and I'm not aware of any requirement to notify the OEM when someone applies for an STC.  You have to remember that many STCs are for airplanes who's manufacturers disappeared long ago, so you really can't make that a basic requirement.  It's possible however, that the FAA may request OEM input like an NTO for a proposed change on a case by case basis, depending on the scope of the mod, and if OEM cooperation is not forthcoming, it could stymie the STC project.
Certainly there is no requirement for the OEM to support an STC for continuing airworthiness, except perhaps where an STC causes an incident or incidents that generate activity toward an Airworthiness Directive and the OEM's Airworthiness Engineering Department has to get involved.  Operators use to come to us for help with issues on a subsystem installed under an STC, and we'd tell them sorry, we have nothing to do with it.
An OEM that is still in business may, or may not, participate in development of an STC.  One of the difficulties for the STC developer is obtaining engineering Source Control Drawings, which the FAA may require as part of the STC data package.  However, a lot of the time the OEM will want nothing to do with the STC, because it implies (to the OEM's customers) that the OEM will be obligated to help support the mod.
The linked Advisory Circular covers the STC application process and there is no mention of No Technical Objection letters from OEMs or requirements for OEMs to support STCs.  OEMs will sometimes discover STC mods done on their fleet that they had no idea existed until they start to get visibility in service.
STC Application Advisory Circular


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Can someone explain the EASA approval process to fly ETOPS?
First of all does the TC holder (manufacturer) of a new aircraft have to gain approval to state that the aircraft is capable of flying etops to a certain level..? I.e ETOPS 120.
Secondly does the operator have to then show compliance to show they are maintaining the aircraft for ETOPS operation to gain certification within their AOC?
So can you have an aircraft for example that is ETOPS capable (from manufacture) but not ETOPS certified if airline aren't maintaining to required standard or have approval from NAA?
Basically I don't understand who has to get the approval, TC holder, operator or both from EASA or the local NAA?
It someone can clarify that would be fantastic..

Related: Can any aircraft have ETOPS? (not a duplicate). Also a summarized ETOPS approbation process, but in French. It references this long EASA document.


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Do large commercial aircraft have keys?
Do the likes of 737 or a320 or 777 or a380 as examples have keys to the aircraft or to initiate the flight deck? Or are aircraft unlocked and to start the engines it's just a flick of a switch or switches?

There are no keys to anything on a modern airliner. You just get in, hit the switches and go.

Yes but not like a car key.
On the B747s I worked on there was a key to the cockpit door and on combi models there was a key to the main-deck cargo compartment (same key). I still have one somewhere, it's brass and has Boeing stamped on it. These were distributed within the company and all our B747s used the same key.
On the ATR there is also a key for the pax doors but in my airline this is not used as there are ramp guards.
These keys will not stop someone who knows his way around airplanes as there are other panels which can be opened from the outside . Some airlines/authorities required the pax steps/bridge to be removed from unattended widebody aircraft but its common for mechs to access via the avionics compartment. I've never seen a key on these doors.
A more common procedure is to seal all doors and access panels (sticker seals) so that any unauthorised access will be visible and further steps can be taken.. (added checks etc).


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What maintenance actions are required after a bird strike?
Does the SRM or AMM detail what Inspections to do following a bird strike? Do the engineers have to examine the bird remains too and report it to someone?

If there was, you'd find it in AMM Chapter 5, which is where the special inspections are.  If the bird made a major ding or penetrated the structure, there would likely be an incident report and there would be some effort to identify the breed and estimate the size and weight for data gathering purposes.

Depends on the nature of the strike. If a glancing strike—e.g., off the top of the windscreen, or the upper surface of a wing—maybe none is needed. Other strikes could take out the windscreen (some have, in fact).


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Who creates and amends tech logs?
Is it the operator, manufacturer or the NAA?
I'm going to assume the operator does the creation and amending and only the NAA is to approve the document?

I can't answer for EASA, but my experience in north america is the OEM delivers the airplane with a chintzy set of tech logs, like note books, and the operator goes out and buys decent hard bound ones from publishers who produce that kind of stuff.  What goes in the log and how it's to be recorded is a function of local regulations, so the content and formatting just has to conform to those requirements and I've never heard of a regulator approving a tech log as a publication..


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What is a shroud (in aviation terms or engineering terms)?
Please can someone explain what a shroud is and give examples of types of shrouds and their uses on aircraft?

This reads like you're asking us to answer a homework question.

To get a good answer you will need to add a lot more context. The place I've heard the term the most is in the HPT of jet engines, where they are segmented pieces that form the outside wall of the flowpath.

It's "shrouded" in secrecy.  A shroud is something that hides from view.  An access panel hides things from view, but it's main function is as a removable section of an enclosed structure.  A shroud's only job is to block light, heat, fluids, or gases from going from A to B, or to manage where they go.  A shroud on the outside of an airplane who's only function is to manage the airflow for drag reduction is a fairing.
In engineering terms, a shroud is usually a non-structural protective panel, that isn't a fairing or access panel, that "hides" something either from view, from a heat source, some sort of internal flow disturbance, or some potential contaminating substance.
So if I have a an electric actuator I need to protect from the heat of an adjacent bleed air duct, I'll put a panel, a heat shroud, around the actuator or the duct to create a separation between them.  If I have a problem with water migrating through the floor and dripping onto black boxes (which happens a lot in airliners), I may put a shroud over the boxes, basically an umbrella, as a kind of band-aid solution to redirect the water.  I may put a shroud panel over a mass of wiring and plumbing on an engine to protect it from heat, fluids, water, to smooth internal airflow, or just for looks.
Probably the most common use of shrouds on airplanes is as heat shields.  Shrouded ducts, exhaust shrouds, etc.

Maybe worth noting that the original meaning is a burial cloth.

Also, exhaust shrouds for carb heat and cabin heat in light planes.


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Please explain differences between AFM and FCOM manuals?
What are the key differences between AFM and FCOM and where they will be used?

The simple answer is that the AFM is a certification document whose content (procedures, limitations, and performance data) is fundamental to the airplane's certification requirements and is approved (both original and all revisions) by the regulating authority that certified the aircraft. You could say that the AFM is part of the airplane's type certificate.
The FCOM/AOM/Operating Data manual is just a company publication. Its content is not approved. It takes AFM procedures and expands them into a kind of company-recommended procedural framework, provides descriptive information, and provides non-certification related performance data used for planning, like cruise data, optimal profiles etc.

AFM = Aircraft Flight Manual
FCOM = Flight Crew Operating Manual
The AFM contains data about the plane like performance, procedures, limitations and sometimes data about weight and balance. The AFM is made by the manufacturer and it is specific to a particular MSN.
The FCOM contains the systems, the procedures, the performance.
The FCOM is the "guide" to know how to use the plane: it's the main reference for pilots.

Both the AFM and the FCOM can contain information applicable to a specific variant of tail number, but the AFM is specifically designed for a given aircraft.

AFM, source:
The AFM is the manual designed by the manufacturer, on how to use the aircraft, it has been submitted to the certification authority. It is the reference.

AFM: An aeroplane flight manual (AFM) is a document produced by the
  aircraft manufacturer containing detailed information on the operation
  of the aircraft.
The AFM details the recommended aircraft operating
  technique for normal, abnormal and emergency operation together with
  the Aircraft Performance that should be achieved when the aircraft is
  operated in accordance with these procedures.
The AFM is a vital part of the aircraft inventory and must be carried
  on all flights unless the National Airworthiness Authority (National
  Aviation Authority (NAA)) of the aircraft operator has formally
  accepted that the Operations Manual of the aircraft operator
  replicates all relevant AFM information for an aircraft.
The AFM is
  specific to each aircraft and reflects the precise equipment and
  modification state of that aircraft. In practice, National Aviation
  Authority (NAA) dispensation not to carry the AFM on board an aircraft
  is commonly obtained by commercial aircraft operators.

FCOM, source:
The FCOM is a substitude to the AFM, for how to conduct day to day operations, and is usually designed by the operator (based on the AFM and other manufacturer information). The FCOM can be used for training.

FCOM: Aircraft Operating Manuals/Flight Crew Operating Manuals
  (AOM/FCOM) constitute the primary flight crew reference for the
  operation of an aircraft under normal, abnormal, and emergency
  conditions.
These publications include system descriptions, normal and
  emergency procedures, supplementary techniques, and performance data.
Along with the initial training course, the AOM/FCOM constitutes a
  trainee's first introduction to their new aircraft. This is normally
  followed by fixed-based or full-flight simulator training and,
  ultimately, operating the actual aircraft. Operating manuals must meet
  the needs of initial training, transition training, and line
  operations.

There are other words to name these two manuals, source:

As is often the case in aviation, different manufacturers, different
  National Aviation Authority (NAA), or different users often refer to a
  given item by different names. The naming of aircraft manuals is not
  an exception. This article uses the terms Aircraft Operating Manual
  (AOM) and Flight Crew Operating Manual (FCOM). However, each of these
  designations is interchangeable with other terms. As examples:

Aircraft Operating Manual: This manual might be referred to as Aircraft
  Flight Manual, Airplane Flight Manual or Aeroplane Flight Manual (AFM)
Flight Crew Operating Manual: Also referred to as Aircraft Operating Manual
  (AOM), Aircraft Operating Instructions (AOI) or, more simply,
  Pilot's Manual.

Further confusion arises with the introduction of terms such as
  Operations Manual or Company Operations Manual (COM) which deal with
  how the organisation conducts flight operations and are a requirement
  imposed by the NAA.


text:
How does an operator change the engine thrust rating?
If, for example, an operator has a Boeing 737-800 with CFM56-7B engines set at a 22K thrust rating, but the next operator wanted to operate the engines at 24K thrust rating, what would they need to physically do to the aircraft in order to change this?
Would it involve the engine going to the shop for certain components replacement, or is it as simple as a FADEC reprogram? I've noticed the life of certain engine components differ depending on the thrust rating used so I wondered how the engine is converted to these different configurations?

Please refer to the following website, it explains the plug programming.:
http://nandang-smart.blogspot.com/2014/09/cfm56-7b-identification-plug.html
You may read:

WHEN ENGINES ARE MOVED BETWEEN AIRCRAFT AND MAY REQUIRE A DIFFERENT THRUST INSTALLATION THIS N1 MODIFIER IS USED IN CALCULATIONS TO UPRATE OR DERATE A GIVEN ENGINE AT AN APPROPRIATE LEVEL.

You may also read

THE THRUST LEVEL OF AN ENGINE IS CHANGED (PERHAPS MORE ACCURATELY "PROGRAMMED") BY INSTALLING A "ID PLUG" THAT SCREWS ONTO THE EEC AND CONVEYS PROGRAM INFORMATION THAT SETS THE ENGINE THRUST OUTPUT TO THE LEVEL DESIRED BY THE OPERATOR.

With respect to the thrust limit, you may display on the CDUs ( MCDUs) the FMS thrust limit page that allows the pilots to derate the TO thrust.
The following website shows for the B777 how to get access to the «  thrust limit » page:

So the pilot may change the thrust limit from the CDU, while the rating is changed by pin programming on the plug, the value entered in the CDU by the pilot is transmitted to the FMS which will ask the FADEC to reduce the thrust whatsoever below the rated value chosen by the operator by pin programming.

From the wikipedia page for the CFM56-engine: notice that the different thrust ratings are specified per aircraft type, with for instance the 737-700 having been delivered with four different ratings. The engine hardware for a model number does not change, a reduced maximum rating is indeed just a different circuit board inside the FADEC.
The smaller versions have a lower thrust rating because of the shorter moment arm between vertical tail and engines: upon engine fail, the rudder authority is less and can therefore only compensate for a lower max. thrust.
This article mentions the various ratings, thrust limits, derating etc that are applicable to fixed wing and rotary wing aircraft. Notice the use of the word "rating":

The only  2  thrust ratings that  airplane jet engines are certified for are maximum takeoff (MTO) and maximum continuous  thrust (MCT). All other  thrust ratings —such  as(ground/flight) idle, climb and cruise thrust— are only figures recommended or set by the engine manufacturer.

Beyond what @ymb1 points out about engine certificates, the aircraft type certificates specify the engine model and thrust ratings. The Boeing 737 TCDS provides the approved engine models and thrust options. Operators can't change the engines or thrust ratings without an STC.

Operators cannot change thrust ratings, they can only change thrust limits. If you want higher thrust on your aircraft than the max thrust rating, you have to look at the aircraft type certificate, see if it was certified with an engine or engine mechanical configuration with a higher thrust rating, and if so, swap the engines or convert the engine to a new model configuration. If there is no engine or configuration listed in the TC with a higher thrust rating, then you have to pursue an expensive STC.
I suspect you are confusing thrust ratings (which are design limits from the manufacturer) with thrust limits, which are programmed in the FADEC. Two different things. A turbine engine may be rated for a certain thrust, but be limited to a lower MTO because of the aircraft in which it is installed. The former is fixed and documented on the engine data plate (along with the current configuration of the engine), the latter is programmed into the FADEC.
Turbine engines such as those used on the B737-800 have only two approved thrust ratings, the MTO (max takeoff thrust) and MCT (max continuous thrust). Everything else from there to idle are just manufacturer recommendations. The engines on the -800 are CFM56-7B engines rated at between approximately 18,500 and 34,000 pounds thrust within 49 different model numbers, as listed in the TCDS (Type Certificate Data Sheet). If an operator wants their engines to last, and minimize repair maintenance costs, they will do things like not push the engines to MTO when it is not needed, and less thrust will do.
When anyone adjusts thrust in the FMS for a particular situation, for example, what they are doing is NOT changing thrust rating. What they are doing is changing thrust limits, which the FMS them communicates to FADEC so it knows how to respond to pilot inputs in the throttle quadrant.
For those of you can deal with the FAA's technospeak, AC 33.7-1 goes through the process that an aviation turbine engine manufacturer must follow to obtain type certification, and explains the difference between thrust ratings and operating limitations. In essence, this confirms what I have already stated -- operators cannot change thrust ratings because that would require a new certification process for the engine, with all that that entails. Only limits can be changed and then again strictly within the performance envelope specified in the type certificate.

Why is this answer rated so low, it gave a valid explanation that there are hard thrust ratings that you can't change and adjustable thrust limits that can be changed via FMC.

@Jan, please note the following:  « When engines are moved between aircrafts and may require a different thrust installation  the pin programming N1 modifier is used in calculations to uprate or down rate a given engine at an appropriate level, this has nothing to do with the physical maximum capabilities of the engine. »

@Jan I don't care about the ratings. In web sites like these there are always people who think they know what they speak of, and try to use their votes to silence people who do. Same in Wikipedia and other similar user-moderated spaces.

Why does this answers get delete votes? People may think it is wrong, but that is what the voting system should be used for. Please be reminded that there are two reasons for deleting a question: 1) The answer is extremely low quality: There is little to no scope for improvement. 2)
The answer doesn't attempt to answer the question; it may be a comment or a separate question altogether.
Neither reason applies to this question in my opinion.

That first paragraph seems self contradicting. The first sentence says it can't be done, and then the next sentence explains how it is done.

Hi Juan, this answer is getting better by the minute. Are you perhaps confusing operators with flight crew in your answer? The flight crew (= pilots) can indeed only change the thrust limits (through the FMS), but the operator (airline) can change the thrust ratings (by making their maintenance organisation change the engine configuration, software and paperwork) as explained in your first paragraph (bar the first sentence).

Configuration settings available on the configuration plug do not include thrust settings. That's manufacturer-level, as far as i know. the change of configuration I am talking about requires installation of new components. Are you doing any research or just fishing for a justification to attack the answer?

I am not looking to attack your answer, just looking for ways to improve it. As a matter of fact, I am doing research and I know that for specific engines (e.g. the V2500) the thrust setting can be changes by something similar to a configuration plug. It also requires the installation of a new component (i.e. a new data plate + bracket and nuts & bolts to attach these items to the engine)

@Juan Jimenez, For clarification, the max 100% thrust that shows on the FMS « thrust limit » page corresponds to what is decided by pin programming by the operator and not to the max physical rating of the engine, therefore as an exemple when the pilot reduces  the thrust to 90%, it is 90% of what the operator has chosen by pin programming and not 90% of the max physical limit of the engine.


text:
Help identifying planes from June 20 near Centennial airport in Colorado
I was hiking a couple miles to the west of Centennial airport in Colorado on June 20th, 2024 around 12:15 pm when I heard a large engine that I would have thought was a radial but it sounded like a cylinder was not firing. I thought this was unusual and saw what appeared to be a WWII fighter. A couple minutes later another similar aircraft flew over although the engine did not sound like a radial. That aircraft is pictured here.
I attempted to use Flightradar24 but I am unfamiliar with the usage and could only find a small period of departures. Is this picture good enough to identify the second aircraft type? Is there a way to track down these aircraft another way?

cool photo!!!!!

@Fattie It just goes to show how good modern cameras are on our phones. This is an extreme closeup from a samsung phone.

true, it's madness

Looks like this was most likely P-51D "Crusader" N51JT on this flight.
It didn't sound like a radial because it has a V-12 water cooled engine with an unmistakable sound.
You may wonder how I figured this out...  The photo, while not great, has some P-51 features. In particular, the outlet of the radiator on the belly and the 4-bladed prop -- as well as your description of it not sounding like a radial.
So, I went to the FAA website and did an N-number search for all North American P51's.  That gives a list of registrations by state.  I started with those registered in Colorado.  You can punch each one into FlightAware to find the flights in the past 14 days for any N-number.
This was only the third one from Colorado on the list.
Edit:
Using FlightRadar 24's Playback function, I was able to watch the P-51 flight and click on other aircraft operating in the same time / area.  Lots of Cirrus, Cessnas, and business jets...  One interesting thing was:
This flight of Yak 52 N33YK.  Which has a radial engine.
Edit2:
I now see that there was also a Nanchang Cj-6 N443LM operating at the same time.  At one point (18:45:05 UTC), they cross paths with the Yak.

Interesting research.  Looking further, it appears that while he was doing circles, he flew over a Federal Correctional Institution at fairly low altitude at least once.  Does the USA have regulations regarding such flights, or no?

@EndAntisemiticHate not specifically. How low?

@300D7309EF17 Looking at his flight path, and overlaying ground elevation data for that region, I estimate that he maintained at least 365m (1200ft) above the ground (of course, somewhat less from the rooftops) when flying over that facility.

Is there any way that we can look at planes taking off within a few minutes of this one? I am also interested in finding the first plane I saw if possible. Any other sites I might be able to look at?

@SDH I was unable to find a site that would let me do that.  One would, but it was only listing commercial flights.  Most of these sites have a paid level of access that might let you do what you want.

Actually, I was able to figure out something that should work.  You can use FlightRadar24.  At the bottom of the page, there is the 'Playback' option.  You can reference the P-51's flight to see that it was around the lake at 6:20 PM UTC.  Put 6/20 at 6:20UTC into FlightRadar24 Playback, it will give you a map.  You can scroll to the desired area and then press 'play' to see all traffic in an area.  If you know more precisely where you were, you should be able to figure out what flew overhead -- you should be able to use the P-51 flying over to help narrow the time.

@RobMcDonald Wow, that is amazing. I will play with that. --In response to the edits I don't think it was either of those as the distinctive feature for me was a single-seat canopy that was conformed to the fuselage like the original P-51 (no idea what the term for this would be, not a bubble canopy). But the sound of the engine was off, it definitely sounded like it was not firing on a cylinder. Then just two minutes later this other plane came over and I was able to get the phone out in time to get a picture. I figured they were flying together but could have been wrong.

Before switching to the bubble canopy of the P-51D (and later), the A-C models had a 'razorback' canopy.  Similarly, the early P-47 had a razorback before switching to a bubble canopy.  Many other aircraft had a similar design (P-40, BF109, Spitfire, Hellcat, Wildcat, etc), but in my experience they were only called a razorback on the P-51 and P-47.

@RobMcDonald I was able to get the playback working and saw the flight of 51. Oddly the aircraft that flew over me two minutes prior does not show at all on the playback so it will remain a mystery. Thanks for explaining the tool usage to me. I could not find the playback button initially because my browser was not maximized. The website thinks it is a mobile browser when you resize it for some reason.

When flying VFR (visual flight rules, good weather), registering yourself with ATC is optional.  This service is called 'Flight Following' and is often not used by recreational pilots on local area flights.  Systems like FlightAware and FlightRadar24  only know about IFR flights and flights with Flight Following selected.  It is not very surprising that your other flight did not elect to use flight following.  If they are local, maybe you'll see them again.  Happy plane watching!


text:
Any instances of circular wings in full scale gliders/airplanes?
As a kid building from The Great International Paper Airplane Book I was intrigued by the very unconventional plane seen near the bottom of this page with the two circular wings connected by a rigid tube body:
paper airplanes
I am not sure if they are even considered wings in the conventional sense. Has something like that been used on a full-size aircraft? I almost think it could be scaled up as a life-saving device for certain situations.

This answer should be helpful and maybe it even answers your question.

@sophit I see the term is closed wing. Still not sure if I would call it a wing if it is not producing any lift.

Airflow at a given angle of attack will produce lift over many "unconventional" surfaces, just not as efficiently as a classic wing.
Low weight makes many creative forms possible with paper airplanes.
Low Reynolds numbers and strength considerations also change design parameters towards lower aspect ratios.
But this "double tube" glider does share commonality with other aircraft with its fore and aft airfoils.
Most importantly, it shows that circular shapes can create lift.  Scaled up to a fan jet with high speed air intake, flying at low airspeeds and high AoA, the lift created by the nacelle may have a significant effect on the pitching properties of the aircraft if placed too far away from the center of gravity.
The channel wing was actually patented in 1929 by Willard Custer and flown in 1942 as the CCW-1.

Up until the 1950s or so, engineers would sometimes build things simply because they were curious or desperate and because nobody had yet guaranteed that they wouldn't work. Thank goodness. https://en.m.wikipedia.org/wiki/Coleopter

That is about the scariest aircraft I have ever seen.

SDH - https://en.m.wikipedia.org/wiki/De_Lackner_HZ-1_Aerocycle

I take it back. This is much scarier. And I jump out of perfectly good airplanes for fun.


text:
Any light aerobatic aircraft suitable for a first aircraft after getting pilot's license?
I plan on getting my pilot's license next spring and purchase an aircraft. My intention is to purchase an aircraft capable of light aerobatics but with flight characteristics suitable for a beginner. I will not be jumping into aerobatics but will take my time in a safe manner. My question is are there light aerobatic aircraft that would be suitable for this scenario?

Light in what sense? LSA compatible, or simply "not heavy"?

@KennSebesta I was referring to the aerobatic capabilities not the weight. Not sure what LSA refers to.

LSA refers to Light Sport Aircraft, which is a category of airplanes in the EASA and FAA systems (with some slight differences). Basically, ~600kg MTOW and there are easier regulations which can apply.

There is the Citabria to consider.

Wow, +5 gs. I would not have expected that.

+1. I have competed in aerobatics competitions with a Citabria. Indeed, the 7ECA model is considered the reference airplane for the Primary category aerobatics routine. Furthermore, for a long time the Citabria was used as a primary trainer, much like the Cessna 150, so it meets requirements for ease-of-flight.

@KennSebesta I just looked up the definition for that routine. That little plane can fly loops?

Can and does. It's rated for loops, spins, hammerheads, half-cubans, slow rolls, and barrel rolls. I competed in an aerobatics competition this summer, flying a 7ECA.

Citabria is the obvious choice if one only considers certified aircraft. But an RV-4 or RV-6 would do well too.

The Cessna A-152 Aerobat, a C152 structurally strengthened for flying aerobatics, would be a good choice as it is an honest flying aeroplane for doing positive G ‘gentleman’s’ aerobatics in.  This would definitely be my first choice as there is probably going to be a lot of handling characteristics that you are familiar with from flying C152s and C172s in primary flight training.
As mentioned above, the champion Citabria and Decathalon are excellent choices as well.  The Decathalon is equipped with inverted fuel and oil systems so your aerobatic capabilities are expanded quite a bit.  They are also probably the easiest airplanes to transition into flying tailwheel airplanes in.
If you’re interested in going the experimental route, the Vans RV-7/8/14 are very versatile airplanes capable of aerobatic flight and can cruise as fast as 170-180 kts depending on engine choice.  They can also be constructed with either conventional landing gear or a tricycle landing gear configuration, making for better performance on the ground.
One thing to consider be wary of exceeding your capabilities as a pilot, particularly early on as a newly minted private pilot.  Please seek professional instruction on aerobatics and aerobatic flight before attempting this solo.  There are a number of very good schools around the country, Patty Wagstaff’s school down in Saint Augustine FL is perhaps one of the best for upset recovery training, and initial aerobatic training.
Another thing to consider in this purchase as well is the cost of insurance. Any aerobatic capable airplane that can carry passengers i.e. is not a single seat airplane, is going to cost a lot for liability insurance, particularly for a beginner pilot.  You can get around a lot of this by purchasing a single seat, only aircraft such as a Pitts S-1S.  This airplane is a very capable aerobatic aircraft and could be had for around $50,000 if you know where to look. The downside is that it is a very demanding and temperamental tailwheel aircraft and requires a skilled pilot with solid tailwheel time to handle and keep from ground looping.

I was expecting a plug for the Vans Air Force. Sort of the best modern option.

I was hoping someone would mention a P38 or F4U but I guess I can settle for a 152.

You aren’t flying something like that fresh out of primary flight training.

@CarloFelicione That is just a facetious comment.


text:
How do I mount an iPhone X in the cockpit to record flights, as a student pilot?
I'm a student pilot and would like to mount my iPhone X in the cockpit to record my flights. Don't want to get an extra GoPro. However all the mounts I've seen online are designed for iPhone 6 or lower, and the RAM mount seems slightly troublesome to set up, in an aircraft that I'm only spending two hours in every day (and that too not the same aircraft every day).
Any suggestions as to how I can mount my phone? Any help would be appreciated!

What are you planning to record? Views out the window? Of the panel? Of  yourself? Audio too?

You could look at the bean-bag kind of mounts to sit above the panel that have a clip to hold the phone on its sides.  They have non-slip bottom and weighted corners. I first saw these in use with portable GPSs like a Garmin. They work well in a car.  Example https://www.amazon.com/ChargerCity-NonSlip-Smartphone-Beanbag-Friction/dp/B014VWM1F4
I searched for "Beanbag Friction Mount" and then a phone type to find this one.  The beanbag base and the arm ending with a ball look just like the base for my GPS.
Edit: This kind might also work well and be more stable while maneuvering  https://www.amazon.com/dp/B01N210GDQ/ref=sspa_dk_detail_1?psc=1&pd_rd_i=B01N210GDQ&pd_rd_wg=wcjC9&pd_rd_r=QR09DADY9Z9CGFH07G7W&pd_rd_w=Txnpy&smid=APMMY5ZET54AV

I can't see either of these faring well at all in a light aircraft


text:
Why is ground effect greater over smooth hard surfaces?

Helicopter Flying Handbook: Ground effect is the increased efficiency of the rotor system caused
  by interference of the airflow when near the ground. The air pressure
  or density is increased, which acts to decrease the downward velocity
  of air. Ground effect permits relative wind to be more horizontal,
  lift vector to be more vertical, and induced drag to be reduced. These
  conditions allow the rotor system to be more efficient. Maximum ground
  effect is achieved when hovering over smooth hard surfaces. When
  hovering over surfaces as tall grass, trees, brushes, rough terrain,
  and water, maximum ground effect is reduced. Rotor efficiency is
  increased by ground effect to a height of about one rotor diameter
  (measured from the ground to the rotor disk) for most helicopters.
  Since the induced flow vertices are decreased, the AOA is increased,
  which requires a reduced blade pitch angle and a reduction in induced
  drag. This reduces the power required to hover IGE

I understand ground effect and In Ground Effect versus Out of Ground Effect. Air pressure is increased below the helicopter, reducing induced flow, increasing AOA and decreasing drag.
But why is ground effect greater over smooth hard surfaces than over tall grass, trees, bushes, rough terrain, and water?
I've searched Aviation Stack Exchange, textbooks, and the front page of Google, but haven't found an explanation.
At first I would think friction from surfaces like tall grass would hold air below the helicopter, increasing ground effect. But we know this isn't true, since this would mean there's less ground effect over a runway.
Another guess would be the terrain disrupts the air from bouncing back toward the helicopter. Does the air reflect sideways instead, meaning the force of air bouncing back toward the helicopter is what increases lift? The Helicopter Flying Handbook contradicts this explanation with the following as the core source of ground effect:

"The air pressure or density is increased"

Don't be afraid to include complicated aerodynamics if necessary. :)

higly related: What is the effect of uneven ground on ground effect vehicles?

@ManuH This is not the same phenomenon.  In ground effect vehicles, surface irregularities force the vehicle to travel above the peak irregularity, which makes the air cushion less efficient, meaning more power is needed.  In a helicopter, surface irregularities slow and perturb the air, allowing more of that air to recirculate into the rotor, decreasing lift.  Same result, for completely different reasons.

From a conservation of energy perspective, the rotor is transferring energy to the air, which then moves down and is deflected by the ground. A soft or drag-inducing surface will absorb more of that energy, whereas a smooth hard surface will deflect it.
Think of it like running: If you run on a hard surface, your down force creates an equal force up. If you run on sand, some of the down force is lost by moving the sand, and you are not propelled up/forward as much. This is why it is harder to run on sand than a solid surface.

Not to be "that guy" but none of the provided answers are correct.
You got close in your original question when you talked about friction and the air collecting under the helicopter.  But surface friction doesn't help create a better air cushion under the helicopter (that would be good).  Rather, surface friction keeps the air closer to the helicopter, allowing more of it to recirculate into the rotor system.
In a hover, the downwash is flowing vertically down, and as it encounters the surface, it transitions from a vertical downward flow to a horizontal flow spreading out in all directions.  I'll use one of my corny smartboard drawings to illustrate.
Over a smooth surface, this outflowing air travels more easily with less friction, and thus gets farther from the helicopter, making less of it available for recirculation.  (Magenta flow below).
The same downwash over any surface that increases airflow friction, increases the amount of air that decelerates close enough to the helicopter to be recirculated.  (Blue flow below).  Hence you will need more power to produce the same amount of lift.  Less power than OGE, but still more power than a smooth surface.

I think it's based mostly on perception of altitude above ground level. If you're hovering over trees, or over a rough sea, what you care about first and foremost is your clearance from the tops of the trees and waves. And if the surface of the vegetation is dense, like tall crops, trees or bushes, that's what your eyes will focus on, so you perceive that as your height AGL. But for performance purposes, your aerodynamic altitude AGL is actually greater, namely the surface of the ground.
For example, if you're hovering half a rotor diameter above the tree tops, you would perceive that you're close to the ground and might reflexively expect a bit more thrust, but they wouldn't have to be very tall trees for you to be two rotor diameters above ground level, so well out of any aerodynamic ground effect.

The effect is noticeable over a shaggy lawn of just a few inches.

@MaxPower, have you had the chance to test this in a slow hover taxi between a pad and some grass? Most accurate way I think of testing it. It would be worthwhile to walk the surfaces as well to see how level the ground under the grass is (should be at least a little lower than the apron for drainage). In any case, the discussion reminds me of when I used to work on flight sims. As much as we engineers used to grumble about pilots' complaints, when their comments were based on direct observations, they were almost always right. Mixed bag when feedback was based on things they'd read...


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What's the difference between CPM and LDM?
I know CPM is cargo pallet message and LDM is load distribution message, but what's the difference between them ?

Purpose of the LDM is for the load-planner on the next leg of a multi-sector flight knows the figures for the next leg.
Example.. if the flight is routed SIN-DXB-LHR, the LDM from SIN will be broken up into 2 parts, one for SIN-DXB and and one for SIN-LHR. The loadmaster in DXB will use the data in the SIN-LHR part of the LDM telex for his load-sheet and then add in the load joining from DXB.
The CPM is used for aircraft where ULDs are loaded. This will give the loaders info as to which containers are for which destination and also which ULDs contain bags and which contain cargo/mails etc.
A CPM is mandatory for all sectors of ULD equipped aircrafts. An LDM is required for all sectors on all aircraft types except the last sector for an aircraft with ULDs as the CPM is sufficient. As aircraft with only bulk does not have any CPM, the LDM, while not required by most airlines, is still a way to inform the next station of what to expect on the incoming flight.